To map the gravitational field of the satellite had to be made to measure changes in speed of the probe with an accuracy of 5 thousandths of a millimeter per second

A collaboration of Italian and American researchers has achieved a new milestone in the study of the outer solar system, showing how Titan has evolved differently than rocky planets like Earth, and icy satellites such as Ganymede, the interior of which consists of distinct layers. The discovery – made by a team led by Luciano Jesse Department of aerospace engineering and astronautics at the University of Rome “Sapienza”, and which also Paul Racioppi, always of the “Wisdom” and Paolo Tortora of the University of Bologna — was achieved thanks to the measurement of the weak pressure of gravity on the Cassini spacecraft during four close passes of Titan. As was already known to ice and rock composition of Titan, it was necessary to determine the details of the gravity field to know how these materials were distributed within it. Titan – which appears largely as an undifferentiated mixture of water and stones – probably never heated above a temperature of 1000 degrees. The temperature inside the satellite has always been thus too low to make possible the separation of ice and rock. Only 500 kilometers are devoid of the outer rock, while the remaining 2100 kilometers ice and rock are mixed in different percentages depending on the depth. This suggests that Titan, after second-largest satellite Ganymede, has an aggregate rather slowly, perhaps in a million years or more, in a process that began shortly after the formation of the solar system. As is illustrated in an article Science The map of the gravity of Titan has required very precise measurements: Although Cassini is at 1.4 billion cilometri, changes in velocity of the probe were determined with an accuracy of 5 thousandths of a millimeter per second. During the four close passes between 2006 and 2008 the gravity of Titan, Cassini has pushed or slowed in its orbit, and these small accelerations, measured from ground antennas of NASA’s Deep Space Network, showed some irregularities. With the measurements taken by the Cassini spacecraft has drawn the map of the gravity of Titan, which is useful to understand how the topography of the satellite is so little delivered. The ice of Titan must have a temperature at which it allows him to change plastically in response to the weight of mountain ranges, literally sinking into the ice below. The results obtained so far do not indicate clearly whether Titan has an ocean beneath the icy surface, but this hypothesis remains highly plausible. To be able to determine clearly, researchers are working to measure the tides induced by Saturn, a goal that can be obtained during the mission, which ends in 2017 with a plunge into the atmosphere of Saturn.

The close passes the coming years will reveal the thickness of the icy crust and help to understand whether and how liquid methane can come from the atmosphere. Fact, the rivers, lakes and valleys were created by Titan’s liquid methane rains from the clouds in the atmosphere, but its presence requires a source. The methane could be stored and transported to great depths to the surface by convection in the ice, if it is sufficiently flexible and thin.

Source:lescienze.espresso.repubblica.it